This invention relates to flexible elastomer wraps for submerged pilings, risers and pipes, and particularly to such wraps carrying fins protruding therefrom which extend as longitudinal or helical fins or ribs from the periphery of the wrapped submerged piling after the wraps have been deployed and secured thereon in permanent assembly.
Solid objects submerged in and exposed to relative movement of a body of fluid, such as smoke-stacks or overhead cables exposed to wind, or pilings and pipes exposed to ocean currents, produce vortices travelling downstream with the wind or current, sometimes call Von Karman vortex streets accompanied by vibratory movement or aeolian vibrations which may produce resonant vibratory stresses, weakening or damaging the submerged solid structure. Fins protruding from the peripheral surface of the submerged solid object are known to reduce or eliminate such vortex formation, thus minimizing or eliminating any vibratory movement which might be deleterious to the solid structure.
Vibration of chimneys exposed to wind and pilings exposed to ocean currents has been mentioned in numerous United States patents. For example, U.S. Pat. Nos. 3,352,118; 3,383,869 and 4,230,423 all discuss marine pilings but do not suggest that helical ribs could be useful for shedding vortices or minimizing vortex formation. Surface protuberances are suggested in several United States patents, such as U.S. Pat. Nos. 4,193,234; 4,059,129; 3,581,449, 2,604,838 and 3,076,533.
Feis U.S. Pat. No. 4,059,129 shows protrusions formed as segments of helical ribs arrayed in vertical rows on chimneys.
Scruton U.S. Pat. No. 3,076,533 shows helical ribs protruding from the outer surface of chimneys exposed to wind and recommends particular parameters and ratios for the shape of such ribs. For example, Scruton U.S. Pat. No. 3,076,533 shows in its FIG. 3 a wind tunnel model of a chimney with three protruding ribs extending outward from its peripheral surface, at a pitch of approximately 12 times the diameter of the chimney. The text in columns 1 and 4 of this patent mentions that the optimum helix pitch for three equiangularly spaced strakes is of the order of 15 times the diameter or characteristic transverse dimension D. In column 4, ribs or strakes of different heights extending radially from the outer surface of the chimney are described, with heights ranging from 0.029D to 0.118D, stating that at 0.118D the aeolian instability is xe2x80x9creduced to a very small area and only a very small value of structural damping is required to eliminate the oscillations.xe2x80x9d This Scruton patent indicates that round stacks should never require strakes higher than xe2x85x9 of D, even when minimum damping is provided by the solid structure itself.
Helical ribs employed for vortex shedding are suggested for overhead wires or cables exposed to the wind, in Zaltsberg U.S. Pat. No. 4,549,035 and Little U.S. Pat. No. 3,105,866; or for towing lines or towed cables exposed to the ocean in Fabula U.S. Pat. No. 3,884,173 and Cohen U.S. Pat. No. 3,991,550. In each of these four patents a single helical rib or strake is employed, and the relative movement of the body of fluid in which the solid object is immersed is not always transverse to the axis of the object; in all these cases it may be in many different directions, some nearly parallel to the axis of the object itself.
When the ribs, strakes, protuberances and other structures, including piling wraps, described above which are employed to reduce vibration in a submarine environment, such structures are subject to marine growth. Marine growth on such structures alters the original vibration reducing or damping performance characteristics that such structures were designed to have. Accordingly, in some severe cases of marine growth, it is possible that the structures may altogether fail to achieve the intended result.
It has now been discovered that vortex shedding ribs or strakes may be installed on submerged pilings and piping exposed to ocean currents by incorporating these strakes as components of a flexible wrap providing corrosion resistance and biocidal protection for the submerged piling, and which is itself deployed and clamped in position embracing the external surface of the piling or pipe. The strakes may be formed by a pair of clamping flanges mounted along the adjacent edges of parallelogram-shaped wrap segments which are positioned side-by-side encircling the outer surface of the piling or pipe, and then clamped in position.
To deter or inhibit marine growth, the strakes, configured in one embodiment as a pair of clamping flanges or in such other suitable configurations, may be formed as co-extrusion of two layers, an inner layer and an outer layer. The outer layer, which is directly exposed to the submarine environment, incorporates a marine growth inhibiting, or biocide, filler material. By adding precisely controlled quantities, about 5 to 25 weight percent, of the filler material into the starting compound, thermal plastic pellets can be created containing sufficient copper and nickel to provide marine fouling resistance for 10 to 25 years. Both the untreated and treated pellets are separately loaded into the dual hoppers of a co-extruder which during production, produces two separate polymer streams which after passing through a sizing dye, interact to provide, after cooling, a solid extrusion. The inner layer or area provides the original physical design characteristics and the outer layer or area a composite layer of sufficient thickness to render it capable of resisting mechanical damage such as what may be caused during installation or service. It can also prevent marine growth buildup by the release of copper nickel ions from the flake particles or powder contained in the outer layer.
Alternatively, the ribs or strakes, which can be formed as a co-extrusion of two layers, the outer layer incorporating the marine growth inhibiting filler material, may be positioned vertically or diagonally on a flat rectangular panel of flexible wrapping material, dimensioned to encircle by itself a single piling, with clamping flanges mounted along its vertical edges, which can be brought together, stretching the wrap panel by a small but substantial amount, to assure its close embrace around the outer surface of the piling. The wrap is then clamped in this deployed position, thus presenting the strakes in longitudinal or helical configuration encircling the wrapped piling. The strakes themselves may be formed as several different alternative structures. To deter marine growth on the wrap or wrap panels, marine growth inhibiting filler material may be incorporated into the material forming the wrap or wrap panel, or may be incorporated in the outer most layer of material when the wrap or wrap panel is formed from multiple layers.
Accordingly, a principal object of the present invention is to provide wraps for submerged pipes and pilings providing protection against corrosion or damage from marine growths, while also minimizing xe2x80x9cgallopingxe2x80x9d vibratory aeolian movement of the submerged solid object caused by vortices produced by the moving ocean currents.
A further object of the invention is to provide these advantages with flexible wrap panels conveniently installed where required at particular subsurface depths as a retrofitted wrap which eliminates the need for permanent ribs or strakes forming an integral part of the total structure of the submerged pipe or piling.
Another object of the invention is to provide such advantageous features in economical products preferably formed of elastomer sheet material with protruding flexible fins permanently mounted thereon, with the entire elastomer structure being conveniently fabricated, stored, shipped and deployed with minimum expense and minimum labor.
Yet another object of the invention is to prevent the wrap panels, clamping flanges, ribs and strakes from accumulating marine growth.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.